1. Field of Invention
The present invention relates generally to a substrate planarization system and a method for processing a substrate.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to stack multiple devices on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
Two exemplary CMP systems that address these issues are described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov et al. and in U.S. Pat. No. 5,738,574, issued Apr. 15, 1998 to Tolles et al., both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization apparatus that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. The transfer station generally contains a load cup that positions the wafer into one of four processing heads mounted to a carousel. The carousel moves each processing head sequentially over the load cup to receive a wafer. As the processing heads fill, the carousel moves the processing head and wafer through the planarization stations for polishing. The wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry or other polishing fluid medium.
The polishing pad may include an abrasive surface. Additionally, the slurry may contain both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Optionally, one of the planarization stations may be a buffing station. The buffing station also processes the wafer in a motion similar to the planarization station. The buffing station removes surface contamination, such as loosely adhered particles, so that the wafer may be cleaned more effectively after polishing in a cleaning module that may be located adjacent to or remotely from the CMP system.
Another system disclosed in U.S. Pat. No. 5,908,530, issued Jun. 1, 1999, to Hoshizaki et al., which is hereby incorporated by reference, teaches an apparatus for planarizing wafers wherein the wafer is subjected to uniform velocity across the wafer surface with respect to the abrasive surface. The wafer""s motion is provided by a first linear drive and a second linear drive configured to provide x/y motion to a wafer carrier coupled to one of the linear drives. In one aspect, the wafer can be moved in an orbital pattern.
A polishing head is coupled to the wafer carrier to retain the wafer during polishing. Generally, the wafer is positioned in the polishing head by a dedicated load cup that also receives the polished wafers from the polishing head after processing. The polishing head generally stands idle while finished wafers are removed from the load cup and replaced with unpolished wafers.
Since the wafer does not rotate during polishing, all the points on the wafer are subject to a uniform velocity relative to the polishing surface. The uniform velocity across the wafer surface coupled with a multi-programable planarization pattern results in a uniform rate of material removal from the wafer surface. In addition, Hoshizaki et al. provides a number of optional routines that allow a user to fine tune material removal from the wafer.
The systems described above can generally utilize polishing pads with and without abrasive finishes. The polishing pads may be stationary or move relative to the wafer. Additionally, abrasive slurry, de-ionized water and other fluids may be delivered to the polishing pad during wafer processing.
While both the rotational and linear planarization systems have proven to be generally robust polishing platforms, the elimination of the dwell time associated with loading and unloading a polishing head would improve the routing time required to process each wafer, and yield a corresponding increase in wafer throughput (i.e., the number of wafers processed in a unit of time). The increase in wafer throughput has an advantageous effect on both the manufacturing cost of devices fabricated on the wafer, and the cost of ownership associated with the polishing system.
Additionally, compact tool footprints (i.e., the operational area a tool occupies including hardware, access areas and safety buffers) are also desirable. Generally, compact (i.e., small) footprints allow for more processing equipment to be utilized in a given manufacturing area, thus contributing to lower factory overhead and greater wafer throughput.
Therefore, there is a need for an apparatus that provides higher throughput by minimizing the dwell times during wafer transfer between system components while minimizing tool footprint.
One aspect of the present invention generally provides a processing system for polishing a substrate. In one embodiment, a processing system includes a first set of load cups that are nested with a second set of load cups. The second set of load cups are disposed adjacent one or more polishing pads. A first and a second polishing head are coupled to a carrier. The carrier is coupled to a drive system that is adapted to move the first and second polishing heads between positions above the first set of load cups, the second set of load cups and the polishing media. Additionally, a transfer station is provided adjacent the loading cup in at least one embodiment.